Surface-reducing wear occurs in machines by frictional contact of adjacent parts and by other forms of erosion. For example, turbine engines have bearings, shroud liners, combustor liner spring clips, and other areas where reduction wear occurs. Detecting such wear can be critical to safe operation of the machine.
Sensors have been designed to detect wear without disassembly of components. For example, electrical conductors may be embedded in a wear surface. A detector connected to these conductors senses an open circuit caused by wear through a conductor, and determines a wear depth. An example is U.S. Pat. No. 7,270,890.
U.S. Pat. No. 4,884,434 describes loops of optical fibers embedded in a wear surface. Each loop forms an optical circuit with a light source at one end and a detector at the other end. Reduction wear breaks one or more loops in succession, which is detected by respective losses of signal. This design requires enough sensor area for the embedded fibers to form loops, and requires both a source leg and a detector leg of each fiber loop to pass through the sensor block to the source and detector.
U.S. Pat. No. 5,440,395 describes a conical depression in the backside of a shroud liner on the inner surface of a turbine casing. As the shroud is abraded by the rotating turbine blades, the conical depression forms a progressively larger hole in the liner. Light is reflected backward off the conical depression into a detector. Reduction in the reflected light is interpreted via a formula as respective wear depth. However, this device requires a hole in the shroud liner. Entry of combustion gas and particles must be blocked by purge air, which is not needed in the present invention.
U.S. Pat. No. 6,111,643 describes an optical fiber in a wear surface. Light injected into the fiber reflects off the opposed abrading surface and returns through the same fiber. The fiber tip wears along with the wear surface, and the light circuit length is reduced. This length is measured by interferometry to determine a wear depth. The present invention does not analyze reflection from the abrading surface, which requires signal analysis that deals with variable reflectivity, and the present invention does not require interferometry, thus eliminating elements such as reference beam optics.